This invention relates to the field of optical communication systems, and more particularly, this invention relates to an optical communication system using wavelength division multiplexed (WDM) optical communication signals and having back-up receiver capability.
Wavelength division multiplexing (WDM) is commonly used in optical communication systems for increasing the bandwidth of a fiber optic telecommunications link, without increasing the speed of associated electronics. In many prior art optical communication techniques, the bandwidth of a single channel (or wavelength fiber optic telecommunication link) has been limited primarily by the high-speed electronics required at the transmitter and receiver. By using wavelength division multiplexing at a telecommunications system receiver, the optical channels that receive the optical communication signals are separated, or demultiplexed, and sent to individual receivers, which vary in their rate of data receipt. One example of a receiver is a 2.488 Gb/S receiver.
The number of individual receivers used in the optical communications system can vary. These communication receivers connect into a back plane of existing telecommunications equipment. For example, a telecommunications rack could include one or more receivers, such as 8 or 16 receivers, each mounted on a board within the telecommunications rack. When optical components fail, it is necessary to determine the channel that is being used by the failed optical component or particular receiver.
In the past, telecommunication links have rerouted signals on the electrical switching level when any optical components failed, thus loading another path onto the network. It would be more advantageous to re-route an optical communication signal on a particular wavelength channel at the receiver terminal, in the case of a receiver failure or other optical component failure, and not consume network bandwidth as in prior art techniques. This would allow receiver maintenance at any time without increasing downtime or network re-routing.
It would also be desirable to monitor a channel and allow continuous sweeping of the optical communications channels. For example, if a channel showed any signs of weakening or failure, it would be advantageous to identify the source of the problem so that corrective measures could be sought. Thus, there is a need for greater channel monitoring capability. Although there are some channel monitoring devices that use single mode fiber, such as one commercially available system manufactured under the trade designation xe2x80x9cSpectra SPAN,xe2x80x9d it has no capability as a back-up signal receiver.
The present invention is advantageous and allows the re-routing of optical communication signals at the receiver terminal, in case of receiver failure or other optical component failure. The system also does not consume network bandwidth as in past practices, where signals have been re-routed on the electrical switching level when optical components failed. Thus, in the present invention, another path is not loaded onto the network and bandwidth is not consumed. The present invention also allows receiver maintenance at any time, without down time or network re-routing.
The present invention can also function as a channel monitor, allowing continuous sweeping of optical communication channels for quality and performance. When a channel shows signs of weakening or failure, identification of the source of the problem can be triggered, and corrective measures sought. If any one of the dedicated telecommunications system receivers fail on any given wavelength, the back-up receiver system of the present invention can be tuned to that particular wavelength and take over the link, while repairs are being conducted.
The present invention can also be used as a tracking filter for systems that use a tunable laser for laser transmitters that fail. The receiver can track to a new wavelength location where a tunable transmitter has been positioned to account for a failing, or a failed laser transmitter. The present invention can also be used as a tunable receiver for systems/locations requiring tunability, such as add/drop nodes on a fiber.
In accordance with the present invention, an optically amplified back-up receiver system includes an optical splitter positioned along an optical communications path for receiving a wavelength division multiplexed (WDM) optical communications signal and splitting a portion of the WDM optical communications signal into a low power WDM signal onto a back-up path. An optical amplifier receives the low power WDM signal and amplifies same. A tunable filter receives the WDM signal after amplification and selects an optical signal of a desired wavelength that is to be backed-up from the communications path. A receiver section is operatively connected to the tunable filter and receives the selected optical signal and backs up the desired wavelength from the optical communications path. A receiver includes a PIN detector for receiving the optical signal and converts the optical signal into an electrical communications signal.
In one aspect of the present invention, the tunable filter comprises a fiber Fabry Perot filter. The tunable filter also includes a controller operatively connected to the tunable filter in a controller feedback path for controlling the selection of desired wavelengths. An optical/electrical converter, analog/digital converter, and an optical coupler are operatively connected to the tunable filter and controller and convert the optical signals coupled from the optical coupler into digital format for operation within the controller. A digital/analog converter is operatively connected to the controller and tunable filter and receives the control signals from the controller and converts the control signals into the analog signals directed to the tunable filter.
In yet another aspect of the present invention, the optical amplifier includes an injection laser diode and current source control loop circuit connected to the injection laser diode that establishes a fixed current through the injection laser diode. A voltage switcher circuit is connected to the injection laser diode and current source control loop circuit. A voltage switcher circuit is adapted to receive a fixed supply voltage and convert inductively the supply voltage down to a forward voltage for biasing the laser diode and producing an optical fiber coupled laser output.
In yet another aspect of the present invention, the detector includes a PIN photodiode. The receiver section includes an amplifier circuit for amplifying the electrical communications signal and an electronic limiter circuit for reshaping the electrical communications signal. The amplifier circuit also includes a data decision circuit and clock recovery circuit for retiming the electrical communications signal.